A gargantuan clamneck is male OR female fat as a elephant with no desire to reduce their girth, sometimes discovered when a hole gotta be cut in the side of the house for a doctor visit. Funny thing about a true gargantuan clamneck is that when the status has been reached they movement can be so limited that a facilitator is often required a'la MASTER BLASTER relationship...

holy shit my aunt Gerry was so fat she almost sunk da boat,
I think she's a freakin' gargantuan clamneck!